Output control apparatus for laser oscillator

ABSTRACT

A laser oscillator is connected to a power supply device for supplying excitation power to the laser oscillator and a detector is connected to detect the intensity of a laser beam output by the laser oscillator. An apparatus is provided for measuring the resistance value of the detector. A control circuit is operative to provide constant laser power control in response to the detector output under normal conditions but when the output signal of the measuring apparatus indicates a failure, the constant laser output control is changed to the constant power control. The apparatus prevents a constant laser output control from being disabled and workpieces from being defective if the output detector property of a laser changes abruptly.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an output control apparatus for a CO₂gas laser oscillator employed in laser machining, such as cutting, etc.

2. Description of the Background Art

FIG. 7 is a block diagram illustrating the arrangement of an outputcontrol apparatus for a laser oscillator known in the art. In FIG. 7,part of a laser output 3 provided by an output mirror 2a in a laseroscillator 1 is extracted from a rear mirror 2b in the laser oscillator1 and is input to a power sensor 4 constituted by a thermocouple inorder to determine the intensity of the laser output 3. A controlcircuit 5 compares and amplifies an error signal between the value of adesired intensity of the laser output, as given by a laser outputcommand 6, and the value of the output signal (proportional to theintensity of the laser output 3) of the power sensor 4 and provides theresult to a power supply device 8 as a power command 7. Under the powercommand 7, the power supply device 8 supplies the laser oscillator 1with excitation power, whereby laser oscillation is performed. Namely,constant laser output control is carried out by increasing or decreasingthe input power (excitation power) of the laser oscillator so that thelaser output 3 detected and fed back is equal to the laser outputcommand 6.

It is generally known in the output control apparatus for the CO₂ gaslaser oscillator that the power sensor for detecting the laser output isoften constituted by a thermocouple, and its physical property valuechanges with time. In addition, it is known from experience that thechange of the value with time is not linear and the property changesabruptly when it exceeds a given value.

However, the conventional output control apparatus for the laseroscillator is not equipped with a means of measuring the values or therelevant physical properties of the power sensor. Therefore, if animportant property of the power sensor changes suddenly, and in anextreme case, its detection output value is zeroed during, for example,the cutting of a workpiece by the laser oscillator, the constant laseroutput control is disabled, causing all subsequent workpieces to bedefective. Such a fault occurring during the long-time unmannedoperation that often occurs at night presents a serious problem to theuser of the laser oscillator.

It is an object of the present invention to overcome such disadvantages.

An object of the invention is to prevent workpieces from being defectiveif the property of the power sensor makes a sudden change and itsdetection output value changes abruptly.

An object of the invention is to output an alarm signal when theproperty of the power sensor has changed suddenly, thereby specifyingthe changing time of the power sensor.

SUMMARY OF THE INVENTION

In the output control apparatus for the laser oscillator concerned withthe invention, when the resistance value of the laser output detectorhas exceeded a given value, the control circuit operates toautomatically switch from constant laser output control to constantpower control.

In the output control apparatus for the laser oscillator concerned withthe invention, when the resistance value of the laser output detectorhas exceeded a given value, the control circuit operates toautomatically switch constant laser output control mode to constantpower control mode and output an alarm signal to the NC controlapparatus.

In an output control apparatus for a laser oscillator concerned with theinvention, there are connected together a laser oscillator, a powersupply device for supplying excitation power to a laser oscillator, adetector for detecting the intensity of a laser beam output by the laseroscillator, measuring means connected with the detecting means formeasuring the resistance value thereof, and a control circuit forreceiving the output signal of the measuring means output in response tothe output signal of the detecting means and an external laser outputcommand giving the intensity of a laser output to give a power commandto the power supply device. A memory storage is connected with thecontrol circuit and stored with the input/output characteristic of thelaser oscillator. The control circuit has a section which generallyexercises constant laser output control in response to the laser outputcommand and the detector output signal and a section which exercisescontrol by automatically switching the constant laser output controlmode to constant power control mode on the basis of the input/outputcharacteristic of the laser oscillator stored in the memory storage whenthe resistance value of the detector measured by the measuring means hasexceeded a given value.

An output control apparatus for a laser oscillator concerned with thepresent invention is the output control apparatus for the laseroscillator wherein a laser output command section giving the intensityof the laser output is disposed in an NC control apparatus whichcontrols a whole laser cutting system, and a display section fordisplaying a detector changing time in response to the input of a signalgiven by the control circuit when the resistance value of the detectormeasured by a measuring means has exceeded a given value is provided insaid NC control apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating the arrangement of an outputcontrol apparatus for a laser oscillator according to a preferredembodiment of the invention.

FIG. 2 is a block diagram illustrating the details of a part enclosed bya broken line in FIG. 1.

FIG. 3a is a block diagram illustrating a constant power control of alaser oscillator according to the invention and FIG. 3b is anillustration of a stored input/output characteristic.

FIG. 4 is a flowchart to show the steps to detect power sensordeterioration for a laser oscillator according to the invention.

FIG. 5 is a block diagram illustrating the arrangement of an outputcontrol apparatus for a laser oscillator according to a secondembodiment of the invention.

FIG. 6 is a block diagram illustrating the details of a part enclosed bya broken line in FIG. 5.

FIG. 7 is a block diagram illustrating the arrangement of an outputcontrol apparatus for a laser oscillator known in the art.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the invention will now be described with reference tothe appended drawings. Referring to Fig. 1, in a laser oscillator 1,power supplied by a power supply device 8 causes a discharge 1c to occurbetween a pair of electrodes 1a and 1b, exciting a laser medium gas 1dwhich fills the laser oscillator 1. With this excited laser medium gas1d in between, an output mirror 2a is disposed on one side and a rearmirror 2b is provided on the opposite side to constitute an opticalresonator, whereby laser oscillation is generated.

A laser output 3 is provided from the output mirror 2a to the outside ofthe laser oscillator 1. A monitoring output 3a, which is part of thelaser output 3, is extracted from the rear mirror 2b in the laseroscillator 1 and is input to a power sensor 4 constituted by athermocouple, whereby the intensity of the laser output 3 is detected. Acontrol circuit 5 receives the value of a laser output command 6 forgiving the desired intensity of the laser output and the value of theoutput signal of the power sensor 4, compares and amplifies an errorsignal between the two values, and gives the result to a power supplydevice 8 as a power command 7.

Here, a conventional technique for excitation by high frequency silentdischarge is used to excite the laser medium gas 1d. Also, by properlyselecting the discharge gap distance, medium gas pressure and componentratio of the medium gas, the discharge voltage is kept approximatelyconstant.

A well-known mathematical expression for the discharge power is:

    (discharge power=discharge voltage×discharge current).

Accordingly, the value of discharge power is proportional to thedischarge current value for the discharge 1c. Therefore, a currentdetector 8a is provided on a power line connecting the power supplydevice 8 and the electrodes 1a, 1b to detect the discharge current valueof the discharge 1c and feed it back. In this manner, a power levelproportional to the value of the power command 7 can be supplied to thelaser oscillator 1. Namely, the apparatus in the first embodimentexercises constant laser output control by detecting and feeding backthe laser output 3 and by supplying the power to the laser oscillator sothat the laser output value detected and fed back is equal to the laseroutput command 6. In other words, constant laser output control iscarried out by increasing or decreasing the power command value 7.

In FIG. 1, a measuring device 9 is connected to the power sensor 4 inorder to measure the resistance value of the power sensor 4. Thismeasuring device 9 is also connected to the control circuit 5 andoutputs a voltage signal proportional to the measured resistance valueof the power sensor 4 to the control circuit 5.

A memory storage device 10 is connected to the control circuit 5, andits input line and output line are connected with the control circuit 5.The storage device 10 stores the input/output characteristics(relationship between the discharge current Id and the laser output Wr)of the laser oscillator 1 and operates to output an output signal 10b tothe control circuit 5 that is a power command value. That valuecorresponds to the input signal 10a, which is a desired laser outputvalue from the control circuit 5.

FIG. 2 shows the details of a part enclosed by a broken line in FIG. 1.In FIG. 2, 4a denotes a damper for proportionally reducing themonitoring output 3a to a proper output level and 4b represents a powersensor which receives the output of the damper 4a and constituted by athermocouple. A first signal selector 9a is connected to the outputlines of the power sensor 4b and operates to selectively connect theoutput lines of the power sensor 4b to either a first amplifier 5adescribed later or a bridge circuit described later under the control ofthe output signal of a buffer 5l described later. That is, when theoutput signal of the buffer 5l is "1", the output lines of the powersensor 4b are connected to the bridge circuit described later.Alternatively, when the output signal of the buffer 5l is "0", theoutput lines of the power sensor 4b are connected to the first amplifier5a described later. The bridge circuit is constituted by resistors 9b,9c, 9d, and a direct-current voltage source 9e, which applies a voltageto the bridge circuit. When the output lines of the power sensor 4b areconnected to the bridge circuit by the operation of the first signalselector 9a as described above, the resistance value r of the powersensor 4b is given by the following expression:

    r=R(E-2EO)/(E+2EO)(Ω)                                (1)

(where E>2EO, r<R)

r: resistance value of power sensor 4b (Ω)

R: resistance value of resistors 9b, 9c, 9d (Ω)

E: voltage value of direct-current voltage source 9e (V)

E0: voltage value generated between 9f and 9g of bridge circuit (V)

Accordingly, when the values of R and E are known and the value of E0can be calculated, an operation performed according to Expression (1)provides the resistance value r of the power sensor 4b.

The inside of the control circuit 5 will now be described. In FIG. 2,when the output lines of the power sensor 4b have been connected to thefirst amplifier 5a by the operation of the first signal selector 9a asdescribed above, the first amplifier 5a amplifies a very small outputvoltage generated at the thermocouple constituting the power sensor 4b.This very small output voltage is proportional to the output intensityof the laser output 3. 5b is an operator which receives a voltagedeveloped between two points 9f and 9g in the bridge circuit andperforms an operation according to the above Expression (1) to find theresistance value r of the power sensor 4b. 5c designates a comparatorwhich receives the output signal of the operator 5b and a referencevoltage signal 5d. When the output signal value of the operator 5b islarger than or equal to the reference voltage signal value 5d, thecomparator 5c outputs a signal "1 ". Conversely, when the output signalvalue of the operator 5b is smaller than the reference voltage signalvalue 5d, the comparator 5c outputs a signal "0". 5e indicates a knownAND circuit. 5f denotes a latch circuit which receives the output of theAND circuit 5e. The output cf the latch circuit 5f is "0" in the initialstate, but once the input has become "1", the latch circuit it 5foperates to keep the output "1" until it is reset. 5g designates asecond signal selector connected to the output line of the latch circuit5f and designed to selectively connect as the power command 7 either theoutput of an error amplifier 5i described later or the output of thestorage device 10 to the power supply device 8 under the control of theoutput signal of the latch circuit 5f. Namely, when the output signal ofthe latch circuit 5f is "1", the output line 10b of the storage device10 is connected to the power supply device 8 as the power command 7.Alternatively, when the output signal of the latch circuit 5f is "0",the output line of the error amplifier 5i is connected to the powersupply device 8 as the power command 7. 5i indicates the error amplifierwhich outputs to the second signal selector 5g an amplified signalresulting from comparison between the value of the laser output command6 and the value of the output signal of the first amplifier 5a. 5hrepresents a switch which was not shown in FIG. 1 and is designed toselect between "ON/OFF" of the laser output 3 of the laser oscillator 1.When the switch 5h is "closed", power not less than the "thresholdvalue" of laser oscillation is supplied from the power supply device 8to the laser oscillator 1 to provide the laser output 3. This state ishereinafter referred to as "beam ON". Reversely, when the switch 5h is"open", power less than the "threshold value" of laser oscillation issupplied from the power supply device 8 to the laser oscillator 1 andtherefore laser oscillation does not take place and the laser output 3is not provided. This state is hereinafter referred to as "beam OFF". 5jdenotes a control power supply of the control circuit 5 and 5kdesignates a ground of the control power supply 5j. 5l indicates theknown buffer circuit whose input is connected to the switch 5h and whoseoutput is "0" in the "beam ON" state and is "1" in the "beam OFF" state.

The operation of the invention will now be described in accordance withthe arrangement of FIGS. 1 and 2, as well as the flow chart of FIG. 4.Initially, at the start (Step S-1), a determination is made as towhether the beam is On or OFF (Step S-2). When in the ON position, thedetecting operation is not performed (Step S-3). When the beam is OFF,the detecting operation is performed.

When the switch 5h is "closed" or in the "beam ON" state, the power notless than the "threshold value" of the laser oscillation is suppliedfrom the power supply device 8 to the laser oscillator 1 as describedabove, thereby causing the laser oscillation and providing the laseroutput 3. At this time, since the output lines of the power sensor 4bare connected to the first amplifier 5a by the operation of the firstsignal selector 9a, the control circuit 5 outputs to the second signalselector 5g the signal amplified by the error amplifier 5i after acomparison between the value of the laser output command 6 equivalent tothe desired laser output and the value of the output signal of the firstamplifier 5a equivalent to the intensity of the laser output 3. At thistime, because the output signal of the latch circuit 5f is "0", thesecond signal selector 5g has operated to connect the output line of theerror amplifier 5i to the power supply device 8 as the power command(i.e., the discharge current command) 7. That is, in the "beam ON"state, constant laser output control is exercised by increasing ordecreasing the input power (in other words, the discharge current) ofthe laser oscillator so that the laser output 3 detected and fed back isequal to the laser output command 6.

The operation in the "beam OFF" state following Step S-2 will now bedescribed. In the "beam OFF" state, the power less than the "thresholdvalue" of laser oscillation is supplied from the power supply device 8to the laser oscillator 1 as described above, whereby the laseroscillation does not occur and the laser output 3 is not provided. Atthis time, the output lines of the power sensor 4b are connected to thebridge circuit by the operation of the first signal selector 9a (StepS-5). There is a voltage generated between 9f and 9g of the bridgecircuit (Step S-6). The voltage is operated on by the operator 5b tofind the resistance value r of the power sensor 4b (Step S-7). Thecomparator 5c compares the output signal of the operator 5b, i.e., thevoltage value equivalent to the resistance value of the power sensor 4b,with the value of the reference voltage signal 5d acting as a referencefor determining the deterioration of the power sensor 4b (Step S-8).When the output signal value of the operator 5b is larger than or equalto the 5d reference voltage signal value 5d, the comparator 5c outputs asignal "1".

By contrast, when the output signal value of the operator 5b is smallerthan the reference voltage signal value 5d, the comparator 5c outputs asignal "0" (Step S-9). As a result, the AND circuit 5e outputs a "0"(Step S-10) and the output of the latch circuit 5f remains "0" (StepS-11). Then, the output line of the error amplifier 5i is connected tothe power supply device 8 as power command 7 (Step S-12). Hence, whenthe "beam ON" state occurs subsequently, operation is performed toexercise constant laser output control as described above.

In contrast, when in Step S-8 it is determined that the (output signalvalue of the operator 5b) is larger than or equal to the (referencevoltage signal value 5d), the output of the comparator 5c is "1" (StepS-13), and in the "beam OFF" state, the output of the buffer circuit 5lis also "1". Hence, the output of the AND circuit 5e is "1" (Step S-14)and the output of the latch circuit 5f changes to "1" and is latched(Step S-15).

Accordingly, when the "beam ON" state takes place subsequently, thesecond signal selector 5g operates to connect the output line 10b of thestorage device 10 to the power supply device 8 as the power command(i.e., the discharge current command) 7 as described above. Namely, inthe "beam ON" state, the power command (discharge current command) 7equivalent to the desired laser output command 6 is output on the basisof the input/output characteristic (which represents the relationshipbetween the laser output Wr and the discharge current Id) of the laseroscillator 1 stored in the storage device 10 beforehand, wherebyconstant power control is carried out. Here, once changed to "1", theoutput of the latch circuit 5f remains "1" until it is reset (StepS-15), and therefore, the constant power control is kept exercised alsoin the subsequent "beam ON" state (Step S-16).

FIG. 3a is a block diagram to illustrate the case in which constantpower control is exercised as explained above in this embodiment. Theoperation is now described. Control circuit 5 receives the value of alaser output command 6 (i.e., a desired laser output value) and outputsit to storage device 10 as input signal 10a. On the other hand, thestorage device 10 outputs to control circuit 5 an output signal 10bcorresponding to the input signal 10a by basing it on a previouslystored input/output characteristic of the laser oscillator. The storedinput/output characteristic is illustrated in FIG. 3b and may be basedeither on relationship between the laser output Wr and the dischargecurrent Id or on relationship between Wr and the discharge power Wd. Inresponse to the signal 10b, the control circuit 5 provides an output tothe power supply device 8 as a current command (or a power command) 7.The power supply device 8 supplies power to electrodes 1a and 1b and atthe same time, it feeds back the discharge current Id by the currentdetector 8a and exercises control so that the discharge current Id (orthe discharge power Wd) is equal to the current command (or powercommand) 7.

A further embodiment of the invention will now be described withreference to FIG. 5, wherein 11 indicates an NC control apparatus forcontrolling the whole laser cutting system (oscillator, cooler, drivetable, cutting head, etc.).

FIG. 6 shows the details of a part enclosed by a broken line in FIG. 5.In FIG. 5, 5f denotes a latch circuit which receives the output of theAND circuit 5e and 5m represents an output signal of the latch circuit5f and is connected to the NC control apparatus 11. 6 designates a laseroutput command output from the NC control apparatus 11 to the controlcircuit 5 and 5h indicates a beam ON/OFF switch output from the NCcontrol apparatus 11 to the control circuit 5. 11a denotes a displaydevice (such as a CRT) installed on the NC control apparatus 11.

The operation of the invention will now be described in accordance withFIGS. 5 and 6. As in the operation of the first embodiment, when theswitch 5h is "closed", i.e., in the "beam ON" state, the power not lessthan the "threshold value" of the laser oscillation is supplied from thepower supply device 8 to the laser oscillator 1 as described above,thereby generating the laser oscillation and providing the laser output3. At this time, the output lines of the power sensor 4b are connectedto the first amplifier 5a by the operation of the first signal selector9a, whereby the control circuit 5 outputs to the second signal selector5g the signal amplified by the error amplifier 5i after comparisonbetween the value of the laser output command 6 equivalent to thedesired laser output and the value of the output signal of the firstamplifier 5a equivalent to the intensity of the laser output 3 provided.At this time, as the output signal of the latch circuit 5f is "0", thesecond signal selector 5g has operated to connect the output line of theerror amplifier 5i to the power supply device 8 as the power command(discharge current command) 7. Namely, in the "beam ON" state, constantlaser output control is exercised by increasing/decreasing the inputpower (discharge current) of the laser oscillator so that the laseroutput 3 detected and fed back is equal to the laser output command 6.Also, at this time, since the output signal 5m of the latch circuit 5fis "0", i.e., the "power sensor is normal", the display device installedon the NC control apparatus 11 provides no display concerning the powersensor.

The operation in the "beam OFF" state will now be described. In the"beam OFF" state, the power less than the "threshold value" of laseroscillation is supplied from the power supply device 8 to the laseroscillator 1 as described above, whereby the laser oscillation does notoccur and the laser output 3 is not provided. At this time, the outputlines of the power sensor 4b are connected to the bridge circuit by theoperation of the first signal selector 9a and the voltage generatedbetween 9f and 9g of the bridge circuit is operated on by the operator5b to find the resistance value of the power sensor 4b. The comparator5c compares the output signal cf the operator 5b, i.e., the voltagevalue equivalent to the resistance value of the power sensor 4b, withthe value of the reference voltage signal 5d acting as the guideline ofthe deterioration of the power sensor 4b. When the output signal valueof the operator 5b is larger than or equal to the reference voltagesignal value 5d, the comparator 5c outputs a signal "1". By contrast,when the output signal value of the operator 5b is smaller than thereference voltage signal value 5d, the comparator 5c outputs a signal"0".

Now, when the output signal value of the operator 5b is smaller than thereference voltage signal value 5d, the output of the latch circuit 5fremains "0". Hence, when the "beam ON" state occurs subsequently,operation is performed to exercise constant laser output control asdescribed above.

Conversely, when the output signal value of the operator 5b is largerthan or equal to the reference voltage signal value 5d, the output ofthe comparator 5c is "1" and the output of the buffer circuit 5l is alsoHence, the output of the AND circuit 5e is "1" and the output of thelatch circuit 4f changes to "1" and is latched. At this time because theoutput signal 5m of the latch circuit 5f is "1", i.e., the "power sensoris faulty", the display device installed on the NC control apparatus 11displays the "power sensor changing time". Therefore, after the "beamON" state takes place subsequently, the second signal selector 5goperates to connect the output line 10b of the storing means 10 to thepower supply device 8 as the power command (discharge current command)7. That is, in the "beam ON" state, the power command (current command)7 equivalent to the desired laser output command 6 is output on thebasis of the input/output characteristic (which represents therelationship between the laser output Wr and the discharge current Id)of the laser oscillator 1 stored in the storing means 10 beforehand,thereby carrying out constant power control. Here, once changed to "1",the output of the latch circuit 5f remains "1" until it is reset,whereby the constant power control is kept exercised also in thesubsequent "beam ON" state. Similarly, the display device installed onthe NC control apparatus 11 keeps displaying the "power sensor changingtime."

In the output control apparatus for the laser oscillator concerned withthe invention, when the resistance value of the power sensor measured bythe measuring means has exceeded a given value, the control circuitautomatically switches from a constant laser output control mode to aconstant power control mode. Therefore, if the property of the powersensor changes suddenly, its detection output value is zeroed, and theconstant laser output control mode is disabled during the cutting of aworkpiece by the laser oscillator, the invention prevents all workpiecesfrom being defective.

In the output control apparatus for the laser oscillator concerned withthe second embodiment, the control circuit is connected to the NCcontrol apparatus for controlling the whole laser cutting system, andwhen the resistance value of the power sensor measured by said measuringmeans has exceeded a given value, said control circuit automaticallyswitches the constant laser output control mode to the constant powercontrol mode on the basis of the input/output characteristic of thelaser oscillator stored in said storing means and also outputs an alarmsignal to said NC control apparatus, thereby providing a display on thedisplay device on the NC control apparatus. As in the first embodiment,therefore, the second embodiment prevents all workpieces from beingdefective and also makes the power sensor changing time clear, affordingconvenience to laser cutting workers in maintenance.

The entire disclosure of each and every foreign patent application fromwhich the benefit of foreign priority has been claimed in the presentapplication is incorporated herein by reference, as if fully set forth.

Although this invention has been described in at least one preferredembodiment with a certain degree of particularity, it is to beunderstood that the present disclosure of the preferred embodiment hasbeen made only by way of example and that numerous changes in thedetails and arrangement of components may be made without departing fromthe spirit and scope of the invention.

What is claimed is:
 1. An output control apparatus for a laseroscillator, comprising:a laser oscillator; a power supply device forsupplying excitation power to said laser oscillator; a detector fordetecting the intensity of a laser beam output by said laser oscillatorand outputting a signal indicative of said intensity; a measuring meansconnected to said detector for measuring the output value of saiddetector and outputting a measurement signal; and a control circuit forproviding a power command to said power supply device based on saidmeasurement signals and a desired laser output command indicative of adesired intensity of the laser beam output; wherein said power commandoutput by said control circuit indicates operation of the laseroscillator according to a constant power control mode when the measuredoutput value of said detector exceeds a reference value, and otherwiseindicates operation of the laser oscillator according to a constantlaser output control mode; and wherein said power supply device suppliesexcitation power to maintain the laser output to be equivalent to thedesired laser output command when said power command indicates constantlaser output control, and to provide the applied power based on apredetermined value when said power command indicates constant powercontrol.
 2. The output control apparatus for the laser oscillator asdefined in claim 1, further comprising storing means connected with saidcontrol circuit for storing an input/output characteristic of said laseroscillator.
 3. The output control apparatus for the laser oscillator asdefined in claim 2, wherein said predetermined value is based on theinput/output characteristic of said laser oscillator stored in saidstoring means.
 4. The output control apparatus for the laser oscillatoras defined in claim 3, wherein said input/output characteristic is basedon a relationship between the laser output and a discharge current. 5.The output control apparatus for the laser oscillator as defined inclaim 3, wherein said input/output characteristic is based on arelationship between the laser output and a discharge power.
 6. Theoutput control apparatus for the laser oscillator as defined in claim 1,further comprising:a laser output command means for inputting thedesired laser output command, said laser output command means beingdisposed in an NC control apparatus which controls a laser cuttingsystem; and a display means for displaying information regarding changesin said detector measured by said measuring means.
 7. The output controlapparatus for the laser oscillator as defined in claim 6, wherein saidinformation regarding changes in said detector includes a time when ameasured resistance value of said detector exceeds the reference value.8. The output control apparatus for the laser oscillator as defined inclaim 6, wherein said information regarding changes in said detectorinclude a time when said detector changes are measured by said measuringmeans.